The remaining points of disagreement will seem fairly abstruse to anyone who doesn’t follow climate politics closely, but they have important implications. Here are some of the major unresolved questions.

Should the talks’ purpose be to keep the temperature increase since the Industrial Revolution “below” or “well below” 2 degrees Celsius (3.6 degrees Fahrenheit)? Or should there be a more ambitious target of 1.5 degrees Celsius?
(In reality, even a goal of 2 degrees won’t be met. If all the countries here were to carry out their emissions pledges, it would result in a long-term increase between 2.7 and 3.5 degrees Celsius. Nonetheless, island states that will face catastrophic consequences even under a 1.5 degree rise have been calling for a stronger target.)

How should the “common but differentiated responsibilities” that countries have accepted, in theory, be met in practice? Rich countries like the United States emphasize the word “common”: Although developed countries have caused the warming of the planet, developing countries now account for nearly two-thirds of emissions. Poorer countries emphasize the word “differentiated,” because they were not historically responsible for the problem. And the poorest countries want the document to emphasize that they will need lots of financial and technological help to meet their goals.

When it comes to fossil fuels, should the long-term goal be “zero greenhouse gas emissions,” “climate neutrality” or “decarbonization”? Oil producers like Saudi Arabia and Venezuela have balked at the word “decarbonization,” which implies a rapid, permanent move away from fossil fuels, even though scientists are in general agreement that the world economy must shift almost exclusively to renewable sources of energy.

Should all countries agree to take steps that are “measurable, reportable and verifiable,” as the United States is strongly pushing for? This is a crucial sticking point. In the absence of a global government, this week’s agreement will be largely based on the honor system. But Mr. Kerry and the European Union want stringent, data-based oversight so that the world will know whether countries are meeting their targets. Many other countries are resisting specifying such a quantified approach.

When it comes to financial and technological help to mitigate and adapt to the effects of climate change, should only rich countries be officially on the hook, or all countries “in a position to do so” (as the United States favors)?

What provisions should be made for “loss and damage” suffered by countries that will suffer long-term damage to their infrastructure, health and even existence as a result of extreme weather?

PARIS — In the 11th hour before the landmark climate deal was approved on Saturday, a few letters threatened to derail years of calculated negotiations and two weeks of intense diplomacy — those that made “should” into “shall.”

Those two words may seem disarmingly similar, but on the international stage, they are worlds apart in terms of the diplomatic meaning they carry. The legally binding “shall” stopped the United States cold when it showed up on Saturday in what was to be the final draft of the historic pact.

Throughout the process, the longer and less binding “should” was a deliberate part of the international agreement, put there to establish that the richest countries, including the United States, felt obligated to pony up money to help poor countries adapt to climate change and make the transition to sustainable energy systems. “Shall” meant something altogether different, American officials said.

When “shall” was spotted in the document on Saturday, Secretary of State John Kerry called his French counterpart and made it clear that unless a switch was made, France could not count on American support for the agreement.

“I said: ‘We cannot do this and we will not do this. And either it changes, or President Obama and the United States will not be able to support this agreement,’ ” Mr. Kerry told reporters after delegates had accepted the deal by consensus Saturday night, amid cheering and the celebratory stamping of feet.

In the world of diplomatic negotiations, seeking a culprit or trying to ferret out ill intention from another party could have spelled doom for an effort that the French and the Americans were equally eager to see succeed.

With talks already running past their Friday deadline, the French conceded the change of wording had simply been “a mistake.” By humbling the “shall” to the status of a typo, it could swiftly be “fixed” and replaced by the more benign “should.”

The fix made, within hours, the 31-page text was presented and adopted. The French had succeeded; the Americans were appeased.

“It was a genuine – it was a mistake,” Mr. Kerry, a seasoned diplomat, said with finality. “I am convinced.”

President François Hollande of France hugged Christiana Figueres, the climate chief of the United Nations, as Ban Ki-moon looked on after the adoption of a climate deal.Credit
Francois Mori/Associated Press

“Unless other regions increase their level of ambition now in line with what the E.U. is already doing, it will not be enough to solve the climate challenge. As long as the E.U. is doing a solo run, our competitiveness remains at risk.”

An earlier version this post incorrectly credited a tweet citing American leadership in the Paris agreement. It was posted on Twitter by @barackobama, an account that is run by the staff of the Organizing for Action group, not President Obama.

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The agreement asks all countries to update targets for reducing emissions by 2020 and every 5 years thereafter.Credit
Kevin Frayer/Getty Images

LE BOURGET, France — The 31-page document that details a landmark agreement reached on Saturday could be a turning point in the struggle to contain global warming, according to several experts who have been scrutinizing the small but momentous changes to the document’s wording.

• It calls for “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.” This language recognizes the scientific conclusions that an increase in atmospheric temperatures of more than 2 degrees Celsius, or 3.6 degrees Fahrenheit, would lock the planet into a future of catastrophic impacts, including rising sea levels, more devastating floods and droughts, widespread food and water shortages and more powerful storms. But it also recognizes the scientific conclusions that warming of just 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, could present an existential threat to low-lying island nations that would be inundated by sea level rise at that rate of increase. But while those nations celebrated the inclusion of that 1.5 degree target, it is more aspirational than practical. The national plans submitted for the conference would probably result in an increase above 3 degrees Celsius.

• To achieve that goal, countries should “reach global peaking of greenhouse gas emissions as soon as possible, recognizing that peaking will take longer for developing country parties, and to undertake rapid reductions thereafter.” Advocates say this wording sends a clear message to the fossil-fuel industry that much of the world’s remaining reserves of coal, oil and gas must stay in the ground and cannot be burned. But the agreement does not call, as a previous version did, for “reaching greenhouse gas emissions neutrality in the second half of the century,” a provision that oil producers fiercely resisted. OPEC states lobbied for language that suggests that at least some fossil fuels can continue to burn, as long as the greenhouse gas emissions are absorbed by a larger number of “greenhouse sinks” such as new forests.

• The agreement acknowledges “the importance of averting, minimizing and addressing loss and damage associated with the adverse effects of climate change.” This was deemed crucial by poor and small-island countries that suffer the most from extreme weather and from long-term impacts like droughts. However, this provision “does not involve or provide a basis for any liability or compensation,” a point that wealthy nations, which did not want to be held financially liable for climate change, insisted on.

• Ahead of the agreement, 186 countries submitted plans detailing how they reduce their greenhouse gas pollution through 2025 or 2030. The agreement requires all countries to submit updated plans that would ratchet up the stringency of emissions by 2020 and every five years thereafter, a time frame that the United States and the European Union urged. India had initially sought a 10-year review cycle.

• The deal requires a global “stocktake” — an overall assessment of how countries are doing in cutting their emissions compared to their national plans – starting in 2023, every five years.

• The deal requires countries to monitor, verify and report their greenhouse gas emissions using the same global system. The United States has insisted that an aggressive system of counting and verifying each nation’s emissions is crucial to the success of any plan. The United States had also pushed for the creation of an outside panel of experts – a sort of “carbon auditor” to verify nations’ emissions reductions. Developing countries, including China and India, had pushed for two separate accounting systems – a more stringent one for rich countries, a more lenient one for poor countries. The United States scored a victory with the inclusion of the single accounting system, but all the details of how it would work, including the creation of the outside verifying body, have been punted to the future.

• The agreement sets up something called a “Capacity-Building Initiative for Transparency” to help developing countries meet a new requirement that they regularly provide a national “inventory report” of human-caused emissions, by source, and track their progress in meeting their national goals.

• The agreement, which takes effect in 2020, calls on nations to establish “a new collective quantified goal” of at least $100 billion a year in climate-related financing by 2020. It avoids a specific number, and even the $100 billion-a-year aspiration is mentioned in the “decision” part of the document, not the “action” section, to avoid triggering a review by the United States Senate. But it makes clear that the $100 billion — promised in 2009 in Copenhagen — is the bare minimum going forward.

• When countries update their commitments, they will commit to the “highest possible ambition,” but the agreement does not set a numeric target. It acknowledges “common but differentiated responsibilities and respective capabilities, in the light of different national circumstances.” This language is essential to a country like India, which believes it will need some time before it can reach peak emissions, given the need to provide 300 million people with electricity. The agreement calls on rich countries to engage in “absolute” reductions in emissions, while calling on developing ones to “continue enhancing their mitigation efforts.”

From left, President François Hollande of France; Laurent Fabius, the French foreign minister; and Secretary General Ban Ki-moon of the United Nations during the climate change conference on Saturday in Le Bourget, near Paris.Credit
Pool photo by Philippe Wojazer

LE BOURGET, France — In soaring rhetoric, the leaders of France and the United Nations called on world leaders to approve the first universal agreement to slow the warming of the planet.

But then they said that the latest version of the long-awaited document — expected at 9 a.m. in Paris, then 10:30 a.m. — was still being translated. So the meeting here was adjourned for lunch, with the document now scheduled to be released at 1:30 p.m., and discussions to resume at 3:45 p.m.

If the scene here, on the 13th day of a conference that was supposed to run for only 12 days, was anticlimactic, it was also quintessentially French: The vocabulary of universal and noble aspirations paired with a practical recognition that clear thinking and harmonious conversation are best facilitated by a night’s rest and a full stomach (preferably with a glass of wine or two).

The French had made a careful decision, after the release of the most recent draft on Thursday night, not to release a new draft until Saturday morning. That meant that exhausted negotiators, who have been up night after night (along with some journalists), were able to catch some Z’s on Friday night. The risk is that the discussions could possibly stretch late into Saturday night, or even Sunday morning.

The lofty rhetoric seemed aimed at avoiding that outcome.

“Our text is the best possible balance — a balance which is powerful yet delicate, which will enable each delegation each group of countries, with his head held high, having achieved something important,” said the French foreign minister, Laurent Fabius, who is presiding over the conference, known as COP21.

He said the planet could not afford a repeat of the last major climate talks, in Copenhagen in 2009, which dissolved in acrimony despite efforts by President Obama and other leaders to forge a deal.

“Nobody here wants a repetition of what happened in Copenhagen,” Mr. Fabius said. “Perhaps not all the planets were aligned, but today they are.”

Ban Ki-moon, the secretary general of the United Nations, said, “The time has come to acknowledge that national interests are best served by acting in the global interest.”

President François Hollande of France called forcefully for an agreement. “This text will, if you should so decide, be the first universal agreement in the history of climate negotiations,” he said. “We will not be judged on a clause or a sentence, but on the text as a whole. We will not be judged on a word but an act — not on a day but a century.”

He added: “There will be no putting this off. There will be no possible postponement. The decisive moment for the planet is here and now.”

Immediately afterward, Mr. Fabius said that the document was still being translated — the United Nations has six official languages — and adjourned he the plenary for a lunch break.

We will not know until Saturday, when the final accord is expected to be shared, if the Paris accord will effectively help shift the global economy from dependence on fossil fuels to renewable energy, thus saving the world’s population from catastrophic climate effects, Ms. Davenport added.

Check in around 9 a.m. Paris time to find out if the 195 countries, along with the European Union, can reach an agreement that has teeth. That is when the French foreign minister, Laurent Fabius, expects an announcement.

But Justin Gillis reported that scientists who were closely monitoring the negotiations said, “the emerging agreement, and the national pledges incorporated into it, are still far too weak to ensure that humanity will avoid dangerous levels of climate change.”

Though climate change is an unusually divisive issue among Americans, a report shows that the United States is the country where the topic is most widely debated by politicians and the public, as the graphic above shows.

In a report published in 2014 by Ipsos Mori, a market research group in the United Kingdom, 16,000 people in 20 countries were asked questions in an online survey about several topics, including climate change. In addition to the United States, respondents came from Britain, Russia, China, India, Brazil, South Africa, Japan, and elsewhere.

According to the report, the United States had more climate change deniers among their respondents than any other country. Britain and Australia each also had a large percentage of respondents who said they did not agree with the notion of human-caused climate change.

In contrast, China, Argentina, Italy, Spain, Turkey, France and India each had more than 80 percent of their respondents say they agreed with the idea of human-caused climate change.

These results supported a finding in a report conducted in 2011 by James Painter from the University of Oxford and the Reuters Institute for the Study of Journalism that suggested that climate skepticism was “predominately an Anglo-Saxon phenomenon.”

The report also suggested that the variations in perspectives in places like the United States, Britain and Australia might be caused in part by the way climate science has been polarized and politicized, especially in the news media, within those countries.

Leaders among the climate change denial movements outside of the United States include Nick Griffin, the former leader of the British National Party; Christopher Monckton, the Third Viscount Monckton of Brenchley; and Tony Abbott, the former prime minister of Australia.